1. The Field of the Invention
The invention concerns a monitoring method for a drive system with a motor and a moving part driven by a motor and more specifically to a system for detecting collisions between a moveable robot and other structure.
2. Related Prior Art
Painting systems for painting vehicle chassis include multi-axis painting robots. The robots include drive systems to control the position of a rotary atomizer. The drive systems include sensors and a controller that emits control signals to motors associated with the robot. The control signals are sent in response to signals received by sensors in accordance with a control program stored in the memory of the controller. The control program is prepared to achieve optimum painting results.
Painting robots can be positioned adjacent other structures. A collision between the painting robot and room boundaries, obstacles, or persons is possible. The collision should be recognized as soon as possible in order to prevent damage to the painting robot, or injury to the persons, or less than desirable painting results. WO98/51453 discloses a monitoring method for a robot that includes collision recognition. In WO98/51453, the reaction of the mechanism to the drive of the robot is evaluated and an error signal is generated as a function of this reaction. For example, if the painting robot bumps against a stationary obstacle like a building wall, then a disturbance force acts on the robot. This force is fed back to the drive so that the drive is halted. For a collision with an elastic obstacle, a disturbance force likewise acts on the robot. Here, however, the force merely leads to slow or inhibit robot motion. However, in each case, the motion quantities of the drive, such as the angular position and the rpm of the motor shaft, deviate at least for a short time from the disturbance-free values.
Thus, known monitoring methods measure the drive-side motion quantities, such as the angular position and rpm of the motor shaft. The error signal generated as a response to collision recognition is calculated from the motion quantities measured on the drive side and the preset regulation or control quantities for controlling the drive and the mechanism.
However, a disadvantage of this known monitoring method for collision recognition is that the mechanical reaction of a collision disturbance force on the drive is strongly reduced by interposed gears. For example, for painting robots, gears with a transmission ratio of 1:100 are used between the drive and the mechanism so that the mechanical reaction of a collision on the drive can be measured only with difficulty. Another disadvantage of known monitoring methods is that incorrect models for the drive lead to large errors, because the reaction of the mechanism to the drive is then set incorrectly. Finally, another disadvantage of known monitoring methods is that the angular position is measured on the drive side, while the acceleration is calculated by differentiating the measured value twice. This second derivative of the measured value leads to a very noisy signal.
Thus, the invention is based on the problem of improving the previously described, known monitoring method for collision recognition so that collision recognition is possible with higher reliability and a quicker reaction time even with interposed gears, for as little measurement expense as possible.